The present invention relates to exhaust gas cleaning equipment comprising scrubber fluid cleaning equipment and a method for cleaning polluted scrubber fluid.
The shipping industry of today strives to reduce harmful emissions, such as emissions originating from the combustion of fuel in the engine, in order to minimize the negative environmental impact and fulfill present and upcoming emission regulations.
One part in this is the reduction in sulphuric oxide (SOx) emissions from ships. Sulphuric oxides are created in the combustion of fuels containing sulphuric residues. The amount of sulphuric oxides in exhaust gas can be reduced by exhaust gas cleaning, e.g. by using scrubbers. The process of cleaning exhaust gas with the aid of the mentioned scrubbers produces polluted scrubber fluid.
Another object is the reductions in nitrogen oxides (NOx) emissions from marine engines. This can be done by implementing Exhaust Gas Recirculation (EGR), where part of the exhaust gas is recirculated to the combustion chamber of the engine. However, the amount of soot and particles in the exhaust gas needs to be decreased. It is therefore desirable to clean the exhaust gas, which can be done by using a scrubber. Also in this process polluted scrubber fluid is produced.
EP 701656 B1 discloses such equipment for recycling and cleaning of exhaust gas in a supercharged internal combustion engine. A scrubber purifies the recycled gas by using scrubber water. The scrubber water is then passed overboard or deposited to a tank for later purification.
The polluted scrubber fluid comprises soot or other organic or inorganic combustion residues. The release of such polluted scrubber fluid into the sea is unacceptable from an environmental point of view and is strictly regulated. On the other hand it is expensive and undesirable to transport larger amounts of waste material to a harbour for disposal.
JP 3868352 B2 discloses equipment for wastewater treatment where polluted seawater from a scrubber is stored in a storage tank and then cleaned using a combination of a centrifugal separator and two oil filters.
One problem is thus to improve the cleaning of the scrubber fluid. One further aspect of improving the cleaning of the scrubber fluid is to minimize the risk of pollutants being carried over from the scrubber fluid back into the exhaust gas where it may cause problems in downstream equipment such as coolers. A further problem is that particles in polluted scrubber fluid tend to adhere on process equipment and piping over time with the risk of a build up of soot scaling resulting in malfunctioning process equipment, sensors, transmitters and the like. Equipment relying on filter technology also has the drawback in the need for surveillance, service and replacement of filter components.